USH2A and retinal degeneration: Mutations in USH2A are the most frequent cause of recessive retinal degeneration in this population with four pedigrees from the current study (RF.VI148.1215, RF.VI145.1215, RF.VI129.0714, and RF.VI127.0514) and two additional pedigrees from our previous studies with causative mutations in USH2A [4].